Avoid creating (const (reg ...)) [PR108603]

convert_memory_address_addr_space_1 has two modes: one in which it
tries to create a self-contained RTL expression (which might fail)
and one in which it can emit new instructions where necessary.

When handling a CONST, the function recurses into the CONST's
operand and then constifies the result.  But that's only valid if
the result is still a self-contained expression.  If new instructions
have been emitted, the expression will refer to the (non-constant)
results of those instructions.

In the PR, this caused us to emit a nonsensical (const (reg ...))
REG_EQUAL note.

gcc/
	PR tree-optimization/108603
	* explow.cc (convert_memory_address_addr_space_1): Only wrap
	the result of a recursive call in a CONST if no instructions
	were emitted.

gcc/testsuite/
	PR tree-optimization/108603
	* gcc.target/aarch64/sve/pr108603.c: New test.

2 files changed, 16 insertions, 3 deletions

diff --git a/gcc/explow.cc b/gcc/explow.cc
index 83439b3..32e9498 100644
--- a/gcc/explow.cc
+++ b/gcc/explow.cc
@@ -349,9 +349,14 @@ convert_memory_address_addr_space_1 (scalar_int_mode to_mode ATTRIBUTE_UNUSED,
       return temp;
 
     case CONST:
-      temp = convert_memory_address_addr_space_1 (to_mode, XEXP (x, 0), as,
-						  true, no_emit);
-      return temp ? gen_rtx_CONST (to_mode, temp) : temp;
+      {
+	auto *last = no_emit ? nullptr : get_last_insn ();
+	temp = convert_memory_address_addr_space_1 (to_mode, XEXP (x, 0), as,
+						    true, no_emit);
+	if (temp && (no_emit || last == get_last_insn ()))
+	  return gen_rtx_CONST (to_mode, temp);
+	return temp;
+      }
 
     case PLUS:
     case MULT:
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/pr108603.c b/gcc/testsuite/gcc.target/aarch64/sve/pr108603.c
new file mode 100644
index 0000000..a2aea9f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/pr108603.c
@@ -0,0 +1,8 @@
+/* { dg-options "-O2 -mabi=ilp32 -fdata-sections" } */
+
+int a[128];
+long long *p;
+void f() {
+  for (long i = 0; i < sizeof(long); i++)
+    p[i] = a[i];
+}